1. Brief Description of the Invention
A method has been developed for the safe generation of metal carbonyl standards for the calibration of iron pentacarbonyl and nickel tetracarbonyl in CO by analylical methods such as FTIR, gas chromatography (GC), and mass spectroscopy (MS). Additionally these compounds can be used for the calibration of other direct introduction spectroscopic systems including but not limited to the sealed inductively coupled plasma (ICP), direct injection ICP-MS, and direct introduction ICP-AES.
2. Related Art
The literature describes two methods to produce pure carbonyls for commercial scale use.
A method for the production of iron carbonyl [Fe(CO).sub.5 ] was described by Walls et al. (U.S. Pat. No. 2,378,053). They described a procedure for the production by passing CO over the metal of the carbonyl desired. The exact conditions of temperature and pressure were found to depend of the particular metal. Walls et al. described that the production of Nickel carbonyl [Ni(CO).sub.4 ] proceeded easier than that for iron carbonyl. Reactions at atmospheric pressure and temperatures not to exceed 50.degree. C. could be used although it was common to use higher temperatures and pressures. It was also recognized that the reaction of Ni+CO and Fe+CO to produce the respective carbonyls proceeded by different kinetic factors. Even in the presence of S or S containing compounds, which were observed to increase the rate of reaction, these processes were deemed impractical for industrial applications by the authors.
British Patent 897,204 describes the preparation of chrome carbonyl [Cr(CO).sub.6 ]. Previous to this patent chrome carbonyls had been formed by direct combination of CO with a salt of the metal in the presence of a strong reducing agent such as Li, Na or lithium aluminum hydroxide. The '204 patent describes preparing the carbonyl from a Cr/Fe alloy which contained less than 40% Cr by weight in the presence of an aromatic sulphonic acid and an alkali metal hydroxide at temperatures between 200-300.degree. C. and pressures between 500-3000 atm. They noted that utilizing chrome alone (not in the presence of an alloy) did not give significant yields. The Cr/Fe alloy produced iron carbonyl and chrome carbonyl.
It has been observed by the present inventors that carbon monoxide (CO) filled in carbon steel vessels has the tendency to produce metal carbonyls, particularly iron carbonyl. There is a need in the semiconductor manufacturing art for determination of Fe and Ni as the carbonyl species in CO. Standards for calibrating laboratory equipment, such as FTIR, GC, ICP, ICP-MS, and ICP-AES, for the determination of metal carbonyl compounds, however are not commercially available. While it is possible to obtain pure iron pentacarbonyl, it is extremely toxic. Nickel tetracarbonyl, however is not stable and is not available as the pure source and is also extremely toxic. In order to prepare a ppm (v/v) standard of iron pentacarbonyl the liquid must be handled. It is not possible to prepare such a standard for nickel tetracarbonyl owing to the unavailability of the source starting material.
It would be a significant advance in the spectroscopic arts if a method were developed for the production of metal carbonyls, such as Fe and Ni carbonyls, at ppm levels which are stable for no less than 2 weeks.